Project Summary: Reproduction is intimately linked to physiological status. Nuclear receptors (NRs) are a family of transcriptional factors with a transcription regulatory N-terminal domain, a DNA-binding domain, and a C-terminal ligand- binding domain. NR ligands include steroid hormones (e.g. estrogen and progesterone), lipids, and other non- polar molecules. NRs are widely expressed and have many roles in reproduction, development and physiology. Abnormal NR signaling contributes to many disease states (including infertility), and mutations in 20 of the 48 known human NRs are associated with genetic disorders. Much remains to be understood, however, regarding the roles of this large family of NRs during oogenesis, and their direct and indirect mechanisms of action. Drosophila melanogaster is a powerful system for investigating fundamental aspects of NR regulation of oogenesis in vivo. Its genome encodes 18 NR homologs representing all of the mammalian subfamilies, it is highly amenable to cell- and tissue-specific genetic manipulations, and has a well characterized ovarian biology. We recently conducted an RNAi-based screen to identify NRs with novel roles in oogenesis. We knocked down individual NRs specifically in adults using a ubiquitous somatic driver, measured egg production, and further analyzed each step of oogenesis. Two major candidates emerged, including HR4 (the homolog of mammalian GCNF) and Syp (the homolog of COUP-TFs). The major goal of this proposal is to investigate the tissue-specific requirements and mechanisms of action for HR4 and Syp in Drosophila oogenesis. NRs can affect and be affected by obesity; therefore, we will also investigate their interactions with fat storage genes. We propose the following specific aims: 1) To determine the tissue-specific requirement and mechanism of action of HR4; 2) to determine the tissue-specific requirement and mechanism of action of Svp, and 3) to determine the effects of adiposity on oogenesis, and examine interactions between adiposity and NRs. Relevance: Reproduction is controlled by physiological factors in our blood circulation, many of which act on cells by binding to molecules called nuclear receptors. We propose to take advantage of powerful research tools in fruitflies to investigate how nuclear receptors acting in various parts of our body can affect the function of the ovary. Because of the high degree of evolutionary conservation of molecules and biological processes between fruitflies and humans, this work will likely provide valuable insights into the normal regulation of oogenesis and how disruption of such processes might lead to reproductive disorders.